Re: [PATCH v1 1/2] MdeModulePkg/SmmCorePerfLib: [CVE-2017-5753] Fix bounds check bypass

["Wu, Hao A" <hao.a.wu@intel.com>]

> -----Original Message-----
> From: Zeng, Star
> Sent: Friday, November 16, 2018 11:14 AM
> To: Wu, Hao A; edk2-devel@lists.01.org
> Cc: Laszlo Ersek; Yao, Jiewen; Zeng, Star
> Subject: Re: [edk2] [PATCH v1 1/2] MdeModulePkg/SmmCorePerfLib: [CVE-
> 2017-5753] Fix bounds check bypass
> 
> On 2018/11/16 9:37, Hao Wu wrote:
> > REF:https://bugzilla.tianocore.org/show_bug.cgi?id=1194
> >
> > Speculative execution is used by processor to avoid having to wait for
> > data to arrive from memory, or for previous operations to finish, the
> > processor may speculate as to what will be executed.
> >
> > If the speculation is incorrect, the speculatively executed instructions
> > might leave hints such as which memory locations have been brought into
> > cache. Malicious actors can use the bounds check bypass method (code
> > gadgets with controlled external inputs) to infer data values that have
> > been used in speculative operations to reveal secrets which should not
> > otherwise be accessed.
> >
> > This commit will focus on the SMI handler(s) registered within the
> > TBD.
> 
> What does the 'TBD' mean here?

Sorry. Patch was generated on the wrong commit, I will send a V2 of the series
to address this.

Best Regards,
Hao Wu

> 
> Thanks,
> Star
> 
> >
> > Hence, this commit adds a AsmLfence() after the boundary/range checks of
> > 'CommBuffer' to prevent the speculative execution.
> >
> > A more detailed explanation of the purpose of commit is under the
> > 'Bounds check bypass mitigation' section of the below link:
> > https://software.intel.com/security-software-guidance/insights/host-
> firmware-speculative-execution-side-channel-mitigation
> >
> > And the document at:
> > https://software.intel.com/security-software-guidance/api-
> app/sites/default/files/337879-analyzing-potential-bounds-Check-bypass-
> vulnerabilities.pdf
> >
> > Cc: Star Zeng <star.zeng@intel.com>
> > Cc: Jiewen Yao <jiewen.yao@intel.com>
> > Cc: Laszlo Ersek <lersek@redhat.com>
> > Contributed-under: TianoCore Contribution Agreement 1.1
> > Signed-off-by: Hao Wu <hao.a.wu@intel.com>
> > ---
> >
> MdeModulePkg/Library/SmmCorePerformanceLib/SmmCorePerformanceLib.c
> | 16 +++++++++++++++-
> >   1 file changed, 15 insertions(+), 1 deletion(-)
> >
> > diff --git
> a/MdeModulePkg/Library/SmmCorePerformanceLib/SmmCorePerformanceLib
> .c
> b/MdeModulePkg/Library/SmmCorePerformanceLib/SmmCorePerformanceLib
> .c
> > index cd1f1a5d5f..63c1eea3a2 100644
> > ---
> a/MdeModulePkg/Library/SmmCorePerformanceLib/SmmCorePerformanceLib
> .c
> > +++
> b/MdeModulePkg/Library/SmmCorePerformanceLib/SmmCorePerformanceLib
> .c
> > @@ -16,7 +16,7 @@
> >
> >    SmmPerformanceHandlerEx(), SmmPerformanceHandler() will receive
> untrusted input and do basic validation.
> >
> > -Copyright (c) 2011 - 2017, Intel Corporation. All rights reserved.<BR>
> > +Copyright (c) 2011 - 2018, Intel Corporation. All rights reserved.<BR>
> >   This program and the accompanying materials
> >   are licensed and made available under the terms and conditions of the BSD
> License
> >   which accompanies this distribution.  The full text of the license may be
> found at
> > @@ -538,6 +538,13 @@ SmmPerformanceHandlerEx (
> >            break;
> >          }
> >
> > +       //
> > +       // The AsmLfence() call here is to ensure the previous range/content
> > +       // checks for the CommBuffer have been completed before calling
> > +       // CopyMem().
> > +       //
> > +       AsmLfence ();
> > +
> >          GaugeEntryExArray = (GAUGE_DATA_ENTRY_EX *) (mGaugeData + 1);
> >
> >          for (Index = 0; Index < NumberOfEntries; Index++) {
> > @@ -650,6 +657,13 @@ SmmPerformanceHandler (
> >            break;
> >          }
> >
> > +       //
> > +       // The AsmLfence() call here is to ensure the previous range/content
> > +       // checks for the CommBuffer have been completed before calling
> > +       // CopyMem().
> > +       //
> > +       AsmLfence ();
> > +
> >          GaugeEntryExArray = (GAUGE_DATA_ENTRY_EX *) (mGaugeData + 1);
> >
> >          for (Index = 0; Index < NumberOfEntries; Index++) {
> >